RailsアプリをHerokuにデプロイするとビルド失敗する

Question

Herokuへのデプロイでエラー

ID aa650cdb-14c9-4ee2-bb3f-14b283690d88
 !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
			Detected buildpacks: Ruby,Node.js
			See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.5.0
-----> Installing dependencies using bundler 1.15.2
       Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
       Warning: the running version of Bundler (1.15.2) is older than the version that created the lockfile (1.17.1). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
       Fetching gem metadata from https://rubygems.org/............
       Fetching version metadata from https://rubygems.org/..
       Fetching dependency metadata from https://rubygems.org/.
       (中略)
       Installing activerecord 5.2.1.1
       Fetching actionpack 5.2.1.1
       Installing actionpack 5.2.1.1
       Fetching actioncable 5.2.1.1
       Fetching actionmailer 5.2.1.1
       Fetching activestorage 5.2.1.1
       Installing actionmailer 5.2.1.1
       Installing activestorage 5.2.1.1
       Installing actioncable 5.2.1.1
       Fetching railties 5.2.1.1
       Installing railties 5.2.1.1
       Fetching sprockets-rails 3.2.1
       Installing sprockets-rails 3.2.1
       Fetching sass-rails 5.0.7
       Fetching slim-rails 3.1.3
       Fetching rails 5.2.1.1
       Installing rails 5.2.1.1
       Installing slim-rails 3.1.3
       Installing sass-rails 5.0.7
       Bundle complete! 22 Gemfile dependencies, 65 gems now installed.
       Gems in the groups development and test were not installed.
       Bundled gems are installed into ./vendor/bundle.
       Post-install message from sass:
       
       Ruby Sass is deprecated and will be unmaintained as of 26 March 2019.
       
       * If you use Sass as a command-line tool, we recommend using Dart Sass, the new
         primary implementation: https://sass-lang.com/install
       
       * If you use Sass as a plug-in for a Ruby web framework, we recommend using the
         sassc gem: https://github.com/sass/sassc-ruby#readme
       
       * For more details, please refer to the Sass blog:
         http://sass.logdown.com/posts/7081811
       
       Bundle completed (58.54s)
       Cleaning up the bundler cache.
       Warning: the running version of Bundler (1.15.2) is older than the version that created the lockfile (1.17.1). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
       The latest bundler is 2.0.1, but you are currently running 1.15.2.
       To update, run `gem install bundler`
-----> Installing node-v10.14.1-linux-x64
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       Yarn executable was not detected in the system.
       Download Yarn at https://yarnpkg.com/en/docs/install
       I, [2019-03-24T04:57:54.466551 #1621]  INFO -- : Writing /tmp/build_f4e0c88a5f130f145e34942b333f1853/public/assets/favicon-0ad184623fa436976b2f032fcdedec6a55bb67ca4d4423687b91ab36648b399f.ico
       I, [2019-03-24T04:57:54.467003 #1621]  INFO -- : Writing /tmp/build_f4e0c88a5f130f145e34942b333f1853/public/assets/favicon-0ad184623fa436976b2f032fcdedec6a55bb67ca4d4423687b91ab36648b399f.ico.gz
       rake aborted!
       Uglifier::Error: Unexpected token: name (home). To use ES6 syntax, harmony mode must be enabled with Uglifier.new(:harmony => true).
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/uglifier-4.1.20/lib/uglifier.rb:234:in `parse_result'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/uglifier-4.1.20/lib/uglifier.rb:216:in `run_uglifyjs'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/uglifier-4.1.20/lib/uglifier.rb:168:in `compile'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/uglifier_compressor.rb:53:in `call'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/uglifier_compressor.rb:28:in `call'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/processor_utils.rb:75:in `call_processor'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/processor_utils.rb:57:in `block in call_processors'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/processor_utils.rb:56:in `reverse_each'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/processor_utils.rb:56:in `call_processors'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/loader.rb:134:in `load_from_unloaded'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/loader.rb:60:in `block in load'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/loader.rb:317:in `fetch_asset_from_dependency_cache'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/loader.rb:44:in `load'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/cached_environment.rb:20:in `block in initialize'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/cached_environment.rb:47:in `load'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/base.rb:66:in `find_asset'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/base.rb:73:in `find_all_linked_assets'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/manifest.rb:142:in `block in find'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/legacy.rb:114:in `block (2 levels) in logical_paths'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/path_utils.rb:228:in `block in stat_tree'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/path_utils.rb:209:in `each'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/path_utils.rb:209:in `stat_directory'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/path_utils.rb:227:in `stat_tree'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/legacy.rb:105:in `each'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/legacy.rb:105:in `block in logical_paths'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/legacy.rb:104:in `each'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/legacy.rb:104:in `logical_paths'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/manifest.rb:140:in `find'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/sprockets/manifest.rb:186:in `compile'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:68:in `block (3 levels) in define'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-3.7.2/lib/rake/sprocketstask.rb:147:in `with_logger'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:67:in `block (2 levels) in define'
       /tmp/build_f4e0c88a5f130f145e34942b333f1853/vendor/bundle/ruby/2.5.0/gems/rake-12.3.1/exe/rake:27:in `<top (required)>'
       Tasks: TOP => assets:precompile
       (See full trace by running task with --trace)
 !
 !     Precompiling assets failed.
 !
 !     Push rejected, failed to compile Ruby app.
 !     Push failed

HerokuにRailsアプリケーションをデプロイすると、以上のようなエラーが発生し、ビルドが失敗します。
どうすればよいでしょうか。

Answer 1

Uglifier::Error: Unexpected token: name (home). To use ES6 syntax, harmony mode must be enabled with Uglifier.new(:harmony => true).

まずはこのエラーメッセージの指示に従ってみてはどうですか？